Surgical treatment for atrial fibrillation using radiofrequency technology

ABSTRACT

Ablation systems and methods for treating atrial fibrillation utilizing RF energy are provided. The system generally includes a first conductive member having a shape which defines a desired lesion pattern or a portion of a desired lesion pattern, and a second conductive member effective to transmit ablative radiation to the first conductive member. The first conductive member is adapted to be positioned on a first tissue surface, and the second conductive member is adapted to be positioned on a second, opposed tissue surface. In use, ablative radiation is transmitted from the second conductive member through the tissue to the first conductive member to form a lesion having the desired lesion pattern.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 10/434,660,filed May 8, 2003, which is a continuation of application Ser. No.09/966,756, filed Sep. 28, 2001, both entitled “Surgical Treatment forAtrial Fibrillation Using Radiofrequency Technology,” and both of whichare hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to instruments and methods for treatingatrial fibrillation, and more particularly to a surgical instrument andmethod for ablating cardiac tissue using radiofrequency energy.

BACKGROUND OF THE INVENTION

Cardiac arrhythmias, such as atrial fibrillation, are a commonlyoccurring disorder characterized by erratic beating of the heart. Theregular pumping function of the atria is replaced by a disorganized,ineffective quivering caused by chaotic conduction of electrical signalsthrough the upper chambers of the heart. While medication can be aneffective treatment for some cases, many patients are not responsive tomedical therapies and require alternative treatment. As an alternativeto medication, a surgical technique, known as the Maze technique,requires open chest surgery to strategically incise the atrial wall, andsubsequently repair the incisions by suturing. The result of thissurgery is to create scar tissue located along the incision lines andextending through the atrial wall to block electrical conductivity fromone segment to another.

While the Maze procedure has proven effective in restoring normal sinusrhythm, it requires considerable prolongation of cardiopulmonary bypassand aortic crossclamp time, especially when performed in combinationwith other open heart procedures. Over the last decade, more simplifiedtechniques have been proposed which replace surgical incisions withablations, or scars, formed in the heart tissue. The various energysources used in ablation technologies include cryogenic, radiofrequency(RF), laser, and microwave energy. The ablation devices are used tocreate tissue lesions in an affected portion of the heart in order toblock electrical conduction.

One common ablation technique employs the use of a catheter that isintroduced into the heart (e.g., intravascularly) to direct RF energy atspecific areas of heart tissue found to be the source of the irregularrhythms. An electrophysiology (EP) study is first performed to discoverthe location and characteristics of the arrhythmia and, once thespecific location is identified and mapped, RF energy is delivered tothe tissue to ablate the tissue, thus forming a lesion that blockselectrical conduction. While minimally invasive techniques are usuallypreferred, the procedure is often performed in combination with otheropen heart procedures as a prophylactic to prevent post-operative onsetof atrial fibrillation.

RF ablation techniques are typically successful in treating atrialfibrillation, however the lesions must be well defined within the heartto be effective. The lesion must have a sufficient length, continuityand/or depth to interrupt or to block electrical conduction across theaffected portion of the heart. This can be difficult to achieve withoutforming an incision in the atrium. In addition, if the energy is notuniformly transmitted to the target site, hot spots can form, possiblyleading to severe tissue damage or blood coagulation (clots).

Accordingly, there exists a need for ablation instruments and proceduresthat produce uniform ablations on a retracted atria.

SUMMARY OF THE INVENTION

The present invention provides ablation systems and methods for treatingatrial fibrillation utilizing RF energy. The ablation system generallyincludes two components: a first conductive component adapted to beplaced on or adjacent to a first tissue surface, and a second conductivecomponent adapted to be placed on or adjacent to a second, opposedtissue surface. Both components are effective to communicate with asource of ablative energy. The first component is shaped to conform to adesired lesion pattern, or portion of a lesion pattern. In use, ablativeradiation is transmitted from the second component through the tissue tothe first component to form the desired lesion pattern, or portion of alesion pattern.

In one embodiment, the first component is an elongate conductive memberand the second component is a tissue piercing element. The elongateconductive member is in communication with a source of ablative energyand is adapted to be positioned on a tissue surface. A plurality ofopenings, each having a specific diameter, are formed in the elongateconductive member. The openings can be spaced apart by a distance suchthat, together, the openings form a portion of a lesion pattern. Thetissue piercing element, which is electrically isolated from theelongate conductive member, has a diameter less than the diameter ofeach opening in the conductive member, and is adapted to be deployedthrough each of the openings in the elongate conductive member. In use,the tissue piercing element is effective to transmit ablative energythrough the tissue surface to the conductive member to form a lesionhaving a desired lesion pattern.

The tissue piercing element can include a proximal end and a distal endadapted to be selectively deployed into tissue through each of theplurality of openings. A first conductor element effective tocommunicate with a source of ablative energy can extend from theconductive member, and a second conductor element effective tocommunicate with a source of ablative energy can extend from the tissuepiercing element. In a preferred embodiment, the tissue piercing elementis an energy transmitting electrode and the elongate conductive memberis a return electrode.

In another embodiment, an insulative coating is disposed around thecircumference of each of the plurality of openings in the elongateconductive member, or alternatively such a coating is disposed around aportion of the tissue piercing element. The insulative coating iseffective to electrically isolate the conductive member from the tissuepiercing element.

In yet another embodiment, the elongate conductive member includes a topsurface and a bottom, tissue contacting surface. The bottom surface caninclude an adhesive for selectively securing the elongate conductivemember to tissue. The elongate conductive member can optionally bemalleable to allow the conductive member to be formed into a desiredshape to conform to the tissue on which it is placed, or to form adesired lesion pattern.

In other aspects according to the present invention, the tissue piercingelement includes a flashback lumen extending between a fluid entry portformed on the distal end of the tissue piercing element and a fluid exitport formed on a proximal portion of the tissue piercing element. Theflashback lumen is effective to indicate the position of the distal endof the tissue piercing element when inserted through one of theplurality of openings in the conductive member, thereby providing anindication of the penetration depth.

In another embodiment, the first component of the surgical ablationsystem is a return electrode and the second component is an energytransmitting electrode. The return electrode is movable between a first,retracted position and a second, open position wherein the returnelectrode assumes a substantially circumferential shape. The energytransmitting electrode is effective to transmit ablative radiationbetween intervening tissue and the return electrode member to form asubstantially circumferential lesion pattern. The system can alsoinclude an introducer element having an inner lumen formed therein andbeing adapted to receive the return electrode in the retracted position.

Methods of ablating tissue are also provided. In one embodiment, aconductive member is provided having a plurality of openings and beingeffective to communicate with a source of ablative energy. A tissuepiercing element electrically isolated from the conductive member and incommunication with the source of ablative energy is also provided. Theconductive member is positioned on a first surface of a target tissue,such as cardiac tissue. The tissue piercing element is then deployedthrough a first one of the plurality of openings to position a distalend of the tissue piercing element adjacent a second, opposed surface ofthe target tissue. Once the tissue piercing element is properlypositioned, ablative energy is transmitted between the distal end of thetissue piercing element, intervening target tissue, and the conductivemember to form a lesion segment in the target tissue. The steps ofdeploying the tissue piercing element and transmitting ablative energyare repeated at each of the plurality of openings to form a lesion of adesired size and pattern. Preferably, the openings are spaced apart at adistance such that the plurality of lesion segments overlap to form asingle, elongate lesion.

In another embodiment, an introducer element is provided having an innerlumen formed therein. A return electrode is also provided and iseffective to communicate with a source of ablative energy. The returnelectrode is movable between a first, retracted position wherein thereturn electrode is disposed within the inner lumen of the introducerelement, and a second, open position wherein the return electrode has asubstantially circumferential shape. The introducer element is insertedthrough a tissue surface with the return electrode in the first,retracted position. The return electrode is then moved to the second,open position. Ablative energy is then transmitted between the energytransmitting electrode, intervening target tissue, and the returnelectrode while the energy transmitting electrode is moved around thecircumference of the return electrode, thereby forming a substantiallycircumferential lesion.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is an illustration of a surgical ablation system having aconductive member and a tissue piercing element according to oneembodiment of the present invention;

FIG. 2A is a top view of the conductive member of FIG. 1;

FIG. 2B is a side view of a conductive member according to oneembodiment of the present invention;

FIG. 3A is a side view illustration of a tissue piercing element havinga distal port and an inner lumen according to one embodiment of thepresent invention;

FIG. 3B is a side view illustration of a tissue piercing element havinga recessed distal tip and a depth penetration control according toanother embodiment of the present invention;

FIG. 3C is a side view illustration of a tissue piercing element havinga transverse portion according to yet another embodiment of the presentinvention;

FIG. 4 is an illustration of a surgical ablation system in use having atissue piercing element transmitting ablative energy through a tissuesurface to a conductive member according to one embodiment of thepresent invention;

FIG. 5 is an illustration of the tissue piercing element of FIG. 3C inuse transmitting ablative energy through a tissue surface to aconductive member according to another embodiment of the presentinvention;

FIG. 6 is a schematic representation of an ablation system having anintroducer element inserted through the pulmonary vein of a heart, areturn electrode positioned around the ostia of the pulmonary vein, andan energy transmitting electrode positioned on the epicardial surface ofthe heart according to another embodiment of the present invention; and

FIG. 7 is a side perspective view of the introducer element and returnelectrode of FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides surgical ablation systems and methods fortreating atrial fibrillation. The system and methods are particularlyeffective to form a lesion uniformly through the entire thickness of thetissue, e.g. the myocardial wall, without incising the atria. Themethods can be performed during open-heart surgical procedures, but arepreferably performed using thoracoscopic techniques, wherein the ribsand sternum remain intact and are not significantly retracted duringeach step of the procedure. The techniques according to the presentinvention avoid the need for a gross thoracotomy, and offer more controland precision in treating atrial fibrillation.

The system generally includes a first conductive member having a shapewhich defines a desired lesion pattern or a portion of a desired lesionpattern, and a second conductive member effective to transmit ablativeradiation to the first conductive member. The first conductive member isadapted to be positioned on a first tissue surface, and the secondconductive member is adapted to be positioned on a second, opposedtissue surface. In use, ablative radiation is transmitted between thesecond conductive member, the target tissue, and the first conductivemember to form a lesion having the desired lesion pattern.

For reference purposes, the tissue surface will be referred to herein ashaving a first, outer surface, and a second, inner surface. In apreferred embodiment, the tissue is the myocardial wall of a hearthaving an epicardial outer surface and an endocardial inner surface.

FIG. 1 illustrates one embodiment of the system 10 according to thepresent invention wherein the first conductive member is an elongateconductive member 20, that may be of a plate-like shape, and has aplurality of openings 22 formed therein, and the second conductivemember is a tissue piercing element 30 electrically isolated from theelongate conductive member 20. The elongate conductive member 20 and thetissue piercing element 30 are each adapted to communicate with anablative source of energy 14, and together are effective to ablatetissue. A first conductor element 23A can be provided for electricallycommunicating between the elongate conductive member 20 and the sourceof ablative energy 14, and a second conductor element 23B can beprovided for electrically communicating between the tissue piercingelement 30 and the source of ablative energy 14.

As shown in FIGS. 2A and 2B, the elongate conductive member 20 can haveany shape and size, but preferably has a generally elongate planar shapehaving a top surface 24A, a bottom surface 24B, a first end 26A, and asecond end 26B. The conductive member 20 provides a template for all orpart of a lesion, and thus the shape of the conductive member 20 isdeterminative of the shape or pattern of the lesion, or portion of alesion, to be formed. In an exemplary embodiment, the conductive member20 has a pre-formed shape, and/or is malleable to allow the conductivemember 20 to be formed into a desired shape. By way of non-limitingexample, the conductive member 20 can be formed to have a curvilinear orcircumferential shape to allow the conductive member 20 to be positionedaround all of, or a portion of, the pulmonary veins. As a result, thelesion formed in the tissue will have a curvilinear or circumferentialshape substantially the same as the shape of the conductive member 20.

The elongate conductive member 20 includes a plurality of openings 22formed therein and extending between the top and bottom surfaces 24A,24B. The openings 22 form a template for a lesion pattern to be formedin the tissue. Accordingly, each opening 22 is spaced apart by adistance D, which should be adapted to form a plurality of lesions thatoverlap to form a single, elongate lesion. Preferably, the distance Dbetween each opening 22 should be substantially the same as or less thanthe depth of penetration of the tissue piercing element 30, since thedepth of penetration of the tissue piercing element 30 (FIG. 1) into thetissue is substantially the same as the length of the lesion to beformed. Thus, for example, where the tissue piercing element (FIG. 1) ispenetrated about 5 mm into the tissue, the lesion formed will have alength of about 5 mm, and therefore the distance D between each openingshould be about 5 mm or less than 5 mm in order to ensure that thelesions overlap to form a single, elongate lesion. In a preferredembodiment, the distance D is between about 2 mm and 10 mm, and morepreferably is about 5 mm. Each opening 22 further includes a diameter dand a circumference c, which can vary depending on the diameter d_(t)(FIG. 3A) of the tissue piercing element 30. The diameter d should begreater than the diameter d_(t) of the tissue piercing element 30, andpreferably is between about 0.01 mm and 5 mm.

The elongate conductive member 20 can be made from any electricallyconductive material. Preferred materials include, but are not limitedto, stainless steel, titanium and nickel titanium alloys. The length land width w of the conductive member 20 can vary, but preferably thelength l is in the range of about 10 mm to 75 mm and the width w is inthe range of about 2 mm to 15 mm. The height h (FIG. 2B) of theconductive member 20, which extends between the top surface 24A and thebottom surface 24B, can also vary, but is preferably in the range ofabout 0.1 mm to 2 mm.

In use, the elongate conductive member 20 is adapted to be positioned ona first tissue surface 12A. The bottom surface 24B of the conductivemember 20 can include an adhesive for temporarily securing theconductive member 20 to the tissue surface 12A. Any biologicallycompatible adhesive known in the art can be used for this purpose.Examples of suitable adhesives include hydrocolloid adhesives from 3M,and cyanoacrylates. The conductive member 20 can also optionally includea handle (not shown) for positioning the conductive member 20 on atissue surface 12. Alternatively, or in addition, the conductive member20 can be mated to a stabilizing mechanism effective to stabilize theheart during beating heart surgery. Stabilizing mechanisms are known inthe art and are used to applying a stabilizing force to the heart tominimize the motion of the beating heart during a surgical procedure.

As shown in FIGS. 2A and 2B, the conductive member 20 can include aninsulative coating adapted to electrically isolate the tissue piercingelement 30 from the elongate conductive member 20. Referring to FIG. 2A,the insulative coating 28 can be disposed around the circumference c ofeach opening 22 to prevent contact with the tissue piercing element 30when deployed through an opening 22. Alternatively, as shown in FIG. 2B,the insulative coating 28 can be disposed over the top surface 24A ofthe conductive member 20 and can include a plurality of openings 25having a diameter d₂ slightly less than the diameter d of the pluralityof openings 22 in the conductive member 20. The insulative coating 28can be formed from a variety of materials. Suitable materials includeultra high molecular weight polyethylene, poly tetra fluoro ethylene(Teflon), nylon, parylene and other biocompatible plastics.

The tissue piercing element 30, which is adapted to be deployed througheach of the plurality of openings 22 in the conductive member 20, iseffective to transmit ablative energy between the distal end 34 of thetissue piercing element 30, the target tissue 12, and the elongateconductive member 20 to form a lesion segment in the target tissue 12.As shown in FIGS. 1, and 3A-3C, the tissue piercing element 30 isgenerally an elongate cylindrical member having a proximal end 32, adistal end 34, and optionally at least one inner lumen 36 extendingtherebetween. The distal end 34 of the tissue piercing element 30includes a distal, tissue piercing tip 38, e.g. a needle, which isadapted to be deployed into or through a tissue surface, and theproximal end 32 can include a handle 40 for manipulating the tissuepiercing element 30.

As shown in FIGS. 3A and 3B, the distal tip 38 of the tissue piercingelement has a diameter d_(t) and is adapted to penetrate tissue at adepth d_(p). The diameter d_(t) should be less than the diameter d ofeach opening 22 (FIG. 2A) in the elongate conductive member 22 to allowthe tissue piercing element 30, or at least the distal tip 38 of thetissue piercing element 30, to be inserted through each opening 22.Preferably, the diameter d_(t) is sufficiently small to allow the distalend 38 to puncture the tissue surface 12 without requiring the puncturehole to be sealed after removal of the tissue piercing element 30.Preferably, the diameter d_(t) is equal to or less than 1 mm.

The penetration depth d_(p) of the distal tip 38 is dependent on thedistance between the openings 22 in the elongate conductive member 20,the desired length of the lesion to be formed in the tissue, as well asthe diameters d_(t), d of the tissue piercing element 30 and eachopening 22. As previously indicated, the depth of penetration d_(p)should be substantially the same as the distance between each opening 22in the elongate conductive member 20, and consequently the desiredlength of the lesion to be formed. Preferably, the penetration depthd_(p) of the distal tip 38 is between about 2 mm and 10 mm, and morepreferably is about 5 mm.

FIGS. 3A-3C illustrate a variety of different embodiments of the tissuepiercing element 30 having different features. A person having ordinaryskill in the art will appreciate that the tissue piercing element 30 caninclude any combination of features illustrated and described herein.

In one embodiment, shown in FIG. 3B, the tissue piercing element can berecessed within a housing 42, and movable between a first positionwherein the tip 38 is retracted within the housing 42, and a secondposition, as shown, wherein the tip 38 extends beyond the distal end 42Aof the housing 42. The handle 40 can include an actuating mechanism foractuating the distal tip 38 of the tissue piercing element 30 to movethe distal tip 38 from the first position to the second position,thereby deploying the distal tip 38 into or through a tissue surface 12.A variety of actuating mechanisms can be used including, for example, aslidable lever 48, as shown. Other suitable actuating mechanismsinclude, but are not limited to, spring-actuated pushing assemblies,threaded advancement mechanisms, and pulley assemblies.

In use, the distal end 42A of the housing 42 abuts the outer tissuesurface 12A, thereby preventing penetration of the distal tip 38 of thetissue piercing element 30 beyond the penetration depth d_(p). Thedistance d_(p) that the distal tip 38 is moved beyond the distal end 42Aof the housing 42 is determinative of the penetration depth, which canbe adjustable. By way of non-limiting example, a measurement gauge foradjusting the penetration depth d_(p) can be provided on the handle 40,as shown in FIG. 3B. The measurement gauge can include a plurality ofmarkings 58 to indicate the penetration depth d_(p), and the actuatinglever 48 can be moved based on the desired penetration depth d_(p).Alternatively, or in addition, the distal tip 38 of the tissue piercingelement 30 can be slidably movable to allow the penetration depth d_(p)to be adjusted. A person having ordinary skill in the art willappreciate that a variety of different mechanisms can be used to adjustand/or limit the penetration depth d_(p).

The tissue piercing element 30 can also optionally include a lockingmechanism (not shown) for temporarily locking the tissue piercingelement 30 in the second, deployed position while ablative energy isdelivered to the tissue. The locking mechanism can be, for example, adetent or recess formed in the housing 40 for retaining the actuatinglever 48. A person having ordinary skill in the art will appreciate thata variety of different mechanisms can be provided to lock the tissuepiercing element 30 in the deployed position.

In another embodiment, shown in FIG. 3A, the tissue piercing element 30Acan include a flashback lumen effective to indicate the penetrationdepth d_(p) of the distal tip 38 through the tissue. The flashback lumen36 extends between a distal entry port 44 located at or near the distalend 34 of the tissue piercing element 30A, and an exit port 46 locatedproximal of the distal entry port 44. In one embodiment, the entry port44 is located at a particular distance d_(e) from the distal most tip 38of the tissue piercing element 30A, and the exit port 46 is disposednear the proximal end 32 of the tissue piercing element 30A, as shown,or in the handle 40, or at some other proximal location. In use, thedistal tip 38 is penetrated into tissue, and blood enters the entry port44 when the entry port 44 is inserted just beyond the thickness of thetissue, thereby indicating the position of the distal tip 38 of thetissue piercing element 30A.

The inner lumen 36 of the tissue piercing element 30A can be used tointroduce irrigation and/or cooling fluid to the ablation site.Irrigation fluid is useful for irrigating blood from the ablation site,thereby avoiding or reducing the risk of forming blood clots, andcooling fluid is effective to prevent overheating of the tissue or theformation of hot spots during ablation. Irrigating and/or cooling fluidsare known in the art and include, for example, saline, lactated Ringer'ssolution and sterile water.

FIG. 3C illustrates another embodiment of the tissue piercing element30C, which includes a transverse portion 52 extending from the distalend 34 of the tissue piercing element 30C in a direction transverse tothe longitudinal axis 1 of the tissue piercing element 30C. Thetransverse portion 52, when deployed through tissue, is adapted toextend in a direction adjacent to the inner tissue surface 12B. Aconductive coating 56 can be disposed around a portion substantiallydiametrically opposed to the tissue surface to prevent ablative energyfrom contacting blood flowing adjacent to the inner tissue surface 12B.

A person having ordinary skill in the art will appreciate that thetissue piercing element 30 according to the present invention caninclude some or all of the aforementioned features. In addition, whilean elongate cylindrical member is shown, a person of ordinary skill inthe art will appreciate that the tissue piercing element can have anyshape and size. By way of non-limiting example, the tissue piercingelement can include an array of tissue piercing members, e.g. needles,which are adapted to be disposed simultaneously through each of theplurality of openings in the elongate conductive member 20.Alternatively, the tissue piercing element could be formed integrallywith and electrically isolated from the elongate conductive member.

In use, the tissue piercing element 30 is adapted to be disposed througheach of the plurality of openings in the elongate conductive member 20,and to apply ablative energy through the tissue 12 to the elongateconductive member 20. In order to prevent contact between the tissuepiercing element 30 and the elongate conductive member 20 duringinsertion of the tissue piercing element 30 through one of the openings22, the tissue piercing element can optionally include an insulativecoating. The coating can be formed around the entire length of thetissue piercing element 30, or a distal portion of the tissue piercingelement 30. In the embodiment shown in FIG. 3C, the transverse portion56 preferably includes an insulative coating formed around a portion ofthe transverse member substantially diametrically opposed to the innertissue surface 12B to prevent contact between the transverse portion andany blood flowing adjacent the inner surface 12B of the tissue.

The system 10 according to the present invention can be used on astopped or beating heart, and either during open-heart surgery orthoracoscopic heart surgery. The procedure can be performed eitheralone, or in addition to other surgical procedures. FIG. 4 illustrates across-sectional view of the system 10 in use according to one embodimentof the present invention. The elongate member 20, which includes aninsulative coating 48 formed around the opening 22, is placed on theouter or epicardial surface 12A of the heart 60. A person havingordinary skill in the art will appreciate that, while the presentinvention illustrates the elongate member 20 placed on the outer surface12A of the heart 60, the elongate member 20 can be placed on the inner,endocardial surface of the heart 60. The tissue piercing element 30 isinserted through the opening 22 to position the distal tip 38 at thedesired penetration depth d_(p). Ablative energy 62 is then transmittedbetween the distal tip 38 of the tissue piercing element 30 and theelongate conductive member 20 to ablate intervening tissue and form alesion. Where the embodiment shown in FIG. 3C is employed, the distal,transverse member 52 is inserted through the tissue 12 to position thetransverse portion 52 adjacent the inner, endocardial surface 12B of theheart, as shown in FIG. 5. The insulative coating 56 is shown positionedsubstantially diametrically opposed to the tissue surface to preventcontact between the ablative energy 62 and the blood flowing within theheart 60.

The steps of inserting the tissue piercing element 30 through an opening22 and ablating the tissue are repeated at each of the plurality ofopenings 22 to form a plurality of lesion segments, which together forma lesion pattern 68. The lesion pattern 68 is preferably formed aroundthe pulmonary veins 64 and connected to the mitral valve 66. Theelongate conductive member 20 can be shaped to fit around the pulmonaryveins 64, or it can be moved to form a lesion having the desiredpattern.

In another aspect of the invention, shown in FIG. 6, the firstconductive member of the system 100 is a return electrode 120 and thesecond conductive member is an energy transmitting electrode 130. Firstand second conductors (not shown), e.g. electrically conductive wires,are provided for separately electrically connecting the return electrode120 and the energy transmitting electrode 130 to a source of ablativeenergy. The return electrode 120 is movable between a first, retractedposition (not shown), and a second, open position, as shown in FIG. 6.In use, the return electrode 120 is adapted to be positioned adjacent afirst tissue surface, preferably the endocardial surface of the of apulmonary vein. The energy transmitting electrode 130 is then movedaround a second, opposed tissue surface, preferably the epicardialsurface of the ostia 141, while communicating ablative energy betweenthe tissue and the return electrode to form a circumferential lesion.

The return electrode 120 can have a variety of shapes and sizes, but itpreferably includes a proximal end 126 and a distal, tissue contactingend 128, as shown in FIG. 7. The proximal portion 126 of the returnelectrode 120 has an elongate shape, and the distal portion 128 has acircumferential shape. The distal portion 128 is movable between anopen, circumferential position, as shown, and a retracted position thatenables the return electrode 120 to be inserted through a tissuesurface. In a preferred embodiment, the return electrode 120 is formedfrom a shape memory material and is adapted to collapse into a single,elongate member in the retracted position for inserted or removing thereturn electrode 120 from a tissue surface. Once fully inserted throughor removed from a tissue surface, the return electrode 120 is adapted toexpand into the open position. The return electrode 120 can be malleableto allow the shape of the distal portion 128 to be altered based on thedesired use.

The return electrode 120 can optionally include a tissue piercingportion or tip in the retracted position for inserting the returnelectrode 120 through a tissue surface. An actuating mechanism can beprovided for positioning the return electrode 120 in the retractedposition while inserting and removing the electrode 120 from the tissue.Alternatively, or in addition, an introducer element 122 can be providedfor positioning the return electrode 120 adjacent an inner tissuesurface. The introducer 122 can be a tissue piercing member, such as aneedle, having at least one inner lumen 124 formed therein and adaptedto receive the return electrode 120. The return electrode 120 isdisposable within the inner lumen of the introducer 122 while in theretracted position, and can be moved to the open position after theintroducer 122 is inserted through the tissue.

The return electrode 120 can include an actuating mechanism for movingthe return electrode 120 between the open and retracted positions.Preferably, the return electrode 120 is slidably disposable within theinner lumen 124 of the introducer. A handle or similar grasping elementcan be provided on or near the proximal end 126 of the return electrode120 to move the return electrode 120 between the open and retractedpositions. A person having ordinary skill in the art will appreciatethat a variety of different actuating mechanisms can be provided formoving the return electrode 120 between the open and retractedpositions.

Referring again to FIG. 6, the energy transmitting electrode 130 canhave any shape and size and is adapted to communicate energy through thetissue the return electrode 120. Preferably, the energy transmittingelectrode 130 is a pen-like object having a handle 132 and a distalenergy transmitting end 134. A conductor (not shown) enables the distalenergy transmitting end 134 of the electrode 130 to communicate with asource of ablative energy (not shown).

In use, the return electrode 120 is introduced through a tissue surface,preferably through a pulmonary vein 140, while in the retracted position(not shown). The return electrode 120 can be fully disposed within theinner lumen 124 of the introducer 122 while the introducer 124 isdeployed through the tissue, or alternatively the return electrode 120can be inserted through the introducer 122 after the introducer isinserted through the tissue. The distal end 128 of the return electrodeshould be positioned just beyond the endocardial surface of the ostia141 of the pulmonary vein prior to moving the return electrode 120 tothe open position. Once opened, the proximal end 126 of the returnelectrode can be moved proximally to cause the distal, circumferentialportion 128 to be positioned adjacent the tissue surrounding the ostia141 of the vein. The energy transmitting electrode 130 is then movedaround the epicardial surface of the ostia 141 of the pulmonary veinwhile energy is transmitted through the tissue to the return electrode120, thereby forming a circumferential lesion around the pulmonary vein.A person having ordinary skill in the art will appreciate that thereturn electrode can be positioned around the epicardial surface of thepulmonary vein, or at any other location on the heart, and the energytransmitting electrode 130 can be positioned at an opposed tissuesurface.

One of ordinary skill in the art will appreciate that a variety ofelectrosurgical generators can be used as the energy source. In oneembodiment, the energy source is a radiofrequency (RF) generator thatcan operate in bipolar and/or monopolar mode. Such a generator should becapable of delivering RF energy having from about 1 to 100 watts ofpower and a frequency in the range of about 1 KHz to 1 MHz. Morepreferably, however, the desired frequency is in the range of about 250KHz to 600 KHz, and the desired wattage is in the range of about 10 to50 watts.

One of ordinary skill in the art will appreciate further features andadvantages of the invention based on the above-described embodiments.Accordingly, the invention is not to be limited by what has beenparticularly shown and described, except as indicated by the appendedclaims. All publications and references cited herein are expresslyincorporated herein by reference in their entirety.

1. A method of ablating tissue, comprising: providing a return electrodemember having a substantially circumferential shape; providing an energytransmitting electrode having a distal end effective to communicateablative energy through tissue to the return electrode; positioning thereturn electrode and the energy transmitting electrode on opposed sidesof tissue; and communicating ablative energy between the energytransmitting electrode and the return electrode through the tissue,while moving the energy transmitting electrode around the circumferenceof the return electrode, thereby forming a substantially circumferentiallesion.
 2. The method of claim 1, wherein the return electrode ismovable between an open position and a closed, retracted position, themethod further comprising the steps of introducing the return electrodethrough tissue in the retracted position, and moving the returnelectrode to the open position in which the return electrode has asubstantially circumferential shape.
 3. The method of claim 1, whereinthe return electrode is introduced through tissue via an introducerelement.
 4. The method of claim 3, wherein the introducer element isinserted through a pulmonary vein to position the return electrodearound the endocardial surface of the ostia of the pulmonary vein.